With increasing of electronic industries, electronic devices are developed toward minimization, high operating speed and increasing integration level. As a consequence, the requirement of increasing the pin density of the semiconductor packages becomes more important. A connector, for example, a conductive pin is widely used to electrically and/or structurally interconnect two circuit boards.
Currently, by using a surface mount technology (SMT), circuits or electronic components on two circuit boards are electrically connected with each other via this type of surface-mount connector. Referring to FIG. 1, a schematic exploded view of a circuit board assembly having two circuit boards interconnected by a surface-mount connector according to the prior art is illustrated. As shown in FIG. 1, the circuit board assembly 1 comprises a circuit module 10 and a second circuit board 13. The circuit module 10 includes a first circuit board 11 and multiple connectors 12 (i.e. conductive pins). Several electronic components 111 and 131 are disposed on the first circuit board 11 and the second circuit board 13 respectively. For a purpose of electrically and/or structurally connecting the first circuit board 11 with the second circuit board 13, solder paste 14 is firstly applied to predetermined solder pads on the lower side of the first circuit board 11. Then, the conductive pins 12 are placed on the solder pads of the first circuit board 11. After the first circuit board 11 passes through a reflow furnace (not shown), the conductive pins 12 are securely bonded to the solder pads on the first circuit board 11. Then, solder paste 14 is applied to predetermined solder pads on the upper side of the second circuit board 13 and the conductive pins 12 are placed on the solder pads of the second circuit board 13. After the first circuit board 11 and the second circuit board 13 pass through the reflow furnace (not shown), the conductive pins 12 are securely bonded onto the first circuit board 11 and the second circuit board 13. Meanwhile, the electronic components 111 on the first circuit board 11 and the electronic components 131 on the second circuit board 13 are electrically connected to each other through the conductive pins 12 (i.e. the surface-mount connectors).
The structure of FIG. 1, however, still has some drawbacks. For example, since it is difficult to control the thickness of the solder paste 14, the lower surfaces of the surface-mount connectors 12 are usually not coplanar after the upper surfaces of these surface-mount connectors 12 are bonded on the first circuit 11. The first circuit board 11 of the circuit module 10 is often subject to deformation during the process of passing through the reflow furnace. That is, there is often a height difference h between any two adjacent surface-mount connectors 12. As known, the relatively longer surface-mount connectors 12 and the relatively shorter surface-mount connectors 12 fail to be adjusted to be at the same levels. In a case that the height difference h is greater than the thickness of the solder paste 14 on the second circuit board 13, some surface-mount connectors 12 fail to be in close contact with the solder paste 14 coated on the second circuit board 13 and thus are often suffered from poor solderability. Therefore, the electrical connection and the structural stability between the first circuit 11 and the second circuit board 13 are impaired, and the product yield is reduced.
For avoiding the problem of causing poor solderability between the surface-mount connectors 12 and the second circuit board 13, the height difference h between any two adjacent surface-mount connectors 12 should be adjusted to be as small as possible. Since the thickness of the solder paste 14 on the second circuit board 13 is very small (e.g. about 0.12˜0.15 mm), it is difficult to control the process of fabricating the circuit board assembly.
Therefore, there is a need of providing a circuit module and a circuit board assembly having surface-mount connectors in order to simplify the fabricating process, save cost and avoid poor solderability.